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Does tweaking white LED light give better tomato seedlings?
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In a South Korean trial, tomato seedlings raised for 20 days under a white-plus-red LED with its blue peak moved from 450 nm to 436 nm were leafier and more compact than seedlings under plain white LEDs. Once planted out in a commercial greenhouse, they were ahead on cumulative fruit yield at one early harvest count, but final yield did not differ significantly.
Many white LEDs make their light with a blue chip and a phosphor, and many commercial ones have a pronounced blue peak near 450 nm. A team at Gyeongsang National University asked whether reshaping that white light, by adding red and shifting the blue peak, would raise better tomato seedlings, and whether any head start would still show once the plants were growing and fruiting in a greenhouse (Kang et al., 2026).
What this means for your grow
If you raise tomato seedlings under LEDs, this trial suggests the exact spectrum of a white light can change how leafy and compact the seedlings turn out, even at the same light intensity. It also shows the limits: after transplanting, the advantage showed up only as higher cumulative yield at one early harvest count, and by the end of the season there was no significant difference in yield between the three groups. The authors say the modified (SWR) spectrum may be useful in nursery production for improving some transplant traits, but that marketable yield, lighting costs and whether the result repeats across cultivars and production cycles should be checked.
What did the team do?
Tomato seeds (cultivar Pellinore F1) were sown in 32-cell plug trays of peat moss inside a containerised plant factory at the university's Nae Dong Campus in July 2023. After germinating in the dark, the seedlings spent 20 days under one of three white LED treatments, all at the same light intensity of 275 ± 5 µmol per square metre per second, with 12 hours of light and 12 hours of dark:
- Normal white (NW): a full-spectrum white light with no added red, with its blue peak at 450 nm. This was the control.
- Normal white plus red (NWR): white light with added red, blue peak still at 450 nm.
- Specific white plus red (SWR): white light with added red and the blue peak shifted to 436 nm, which the authors chose because it sits within the absorption region of chlorophyll a and had given different plant responses from 450 nm in earlier studies.
The team measured seedling growth, leaf sugars and other compounds, and the expression of some photosynthesis genes. In August 2023, 16 plants from each treatment were planted into coir in a commercial greenhouse in Sacheon City, where all of them grew under the same conditions. The team then measured leaf photosynthesis, harvested fruit from 26 October to 21 December 2023, and tested fruit from the first truss for soluble solids (Brix), reducing sugars, pH and lycopene.
What did they find?
- Leafier, more compact seedlings under SWR: compared with plain white, SWR seedlings had more leaves (16.5 against 14.5), more leaf area (134 against 105 cm²), heavier leaves (2.4 against 2.0 g fresh weight) and higher compactness (30.3 against 21.9 mg of shoot dry weight per cm of height).
- Not taller: plant height and stem diameter did not differ significantly between treatments, and neither did root weight.
- After transplanting: leaf photosynthesis did not differ significantly between treatments at 40, 54, 68 or 82 days after transplanting.
- Fruit yield: cumulative fruit yield was significantly higher for SWR plants at 78 days after transplanting, early in the harvest, but final cumulative yield at 127 days did not differ between treatments.
- Fruit quality: Brix was highest for the plain white group (6.94%, against 6.86% for NWR and 6.77% for SWR). Lycopene was lower in fruit from NWR plants (7.90 mg per 100 g dry weight) than from plain white (14.2) or SWR (12.2). Reducing sugars and pH did not differ significantly.
What could it mean?
The authors conclude that, at equal light intensity, the SWR spectrum improved selected seedling-quality traits (leaf biomass, leaf number, leaf area and compactness) and was linked to a short-lived early-yield response, but it did not increase final cumulative yield. They suggest SWR may be useful in nursery production for improving some transplant traits, and say practical evaluation should look at marketable yield over set harvest periods, lighting costs and whether the result repeats across cultivars and production cycles. The authors point to seedling nurseries as the main use. It is a single trial, so treat it as an interesting lead for your own seedling setup rather than a reason to change lights.
What were the limitations?
The authors list several. The two red-added lights were not matched apart from the blue peak: they also differed in their mix of red, green and blue light and in their green peak, so the results cannot be put down to 436 nm alone. The study used one cultivar, one light intensity, one photoperiod and one production cycle. Light absorbed by the leaves, seedling-stage gas exchange, chlorophyll fluorescence, protein levels and enzyme activity were not measured. The light treatments stopped at transplanting, after which all plants shared the same partly controlled greenhouse.
Separately, the study was part-funded by Samsung Electronics, and two of the authors work in Samsung Electronics' Lighting Marketing Group; the authors declare no competing interests.
Trial details
- Where: seedling stage in a containerised plant factory at Nae Dong Campus, Gyeongsang National University, South Korea; after transplanting, a commercial greenhouse in Sacheon City, Gyeongsangnam-do, South Korea, with partly controlled temperature and ventilation.
- Who: Gyeongsang National University (Division of Horticultural Science, Department of GreenBio Science and Division of Food Science), with two authors from the Lighting Marketing Group, Samsung Electronics.
- Crop: tomato (Solanum lycopersicum), cultivar Pellinore F1 (Enza Zaden), from seed through to fruiting.
- How long: seedlings sown in July 2023; 20 days of light treatment after germination; transplanted in August 2023; harvest from 26 October to 21 December 2023, with fruit picked every 4 days; final yield assessed at 127 days after transplanting.
- System and substrate: 32-cell plug trays of peat moss for seedlings, watered with 8 L of nutrient solution topped up every three days; in the greenhouse, coir cultivation units, four plants per unit, plants 25 cm apart, grown as single stems on high wires; commercial bumblebee colonies (Bombus ignitus) for pollination.
- Lighting (seedlings): white LEDs at 275 ± 5 µmol m⁻² s⁻¹, 12 hours light and 12 hours dark. Peak wavelengths (red, green, blue): NW 600, 586 and 450 nm; NWR 658, 587 and 450 nm; SWR 658, 579 and 436 nm. Share of light as red, green and blue: NW 26.51%, 46.83% and 26.66%; NWR 47.49%, 33.60% and 18.91%; SWR 45.31%, 35.08% and 19.61%.
- Climate: seeds germinated in the dark at 25 ± 1 °C and 70 ± 5% humidity. Greenhouse temperature, solar radiation and CO2 were logged after transplanting (shown in the paper's Figure 1).
- Nutrition: seedlings, a 1000-fold dilution of a tomato nutrient solution at pH 6.6 and EC 1.8 ± 0.1 dS m⁻¹; greenhouse, pH 5.5 and EC 3.2 ± 0.1 dS m⁻¹.
- Design: three light treatments, each in three separate light compartments with one 32-cell tray (n = 3, six plants measured per tray); after transplanting, 16 plants per treatment in four coir units (n = 4); one-way ANOVA with Duncan's multiple range test at p < 0.05.
- Results: seedlings (NW, NWR, SWR): leaf number 14.5, 14.6 and 16.5; leaf area 105, 102 and 134 cm²; leaf fresh weight 2.0, 2.1 and 2.4 g; leaf dry weight 0.31, 0.36 and 0.41 g; compactness 21.9, 26.3 and 30.3 mg·cm⁻¹; height 15.7, 16.1 and 16.3 cm (not significant). Fruit: Brix 6.94%, 6.86% and 6.77%; lycopene 14.2, 7.90 and 12.2 mg·100 g⁻¹ DW. Cumulative yield higher under SWR at 78 days after transplanting; no difference at 127 days.
- Funding and conflicts: Samsung Electronics (Project in 2023) and the Glocal University 30 Project Fund of Gyeongsang National University in 2024. The authors declare no competing interests.
- Publication: Discover Plants 3:530, published online 10 November 2026, https://doi.org/10.1007/s44372-026-01007-y. Licence: CC BY-NC-ND 4.0.
- Not reported in the paper: temperature and humidity in the seedling compartments during the 20-day light treatment, greenhouse humidity, yield figures in the text (yield is shown only as a graph), and marketable yield.
Links
- The study: Modified white LEDs spectra alter tomato seedling quality and post-transplant responses
- The institution: Gyeongsang National University
References
- Kang, I.-J., Yang, G.-S., Shin, H., Sim, H.-S., Lee, G. O., Jang, S.-N., Cho, D. Y., Cho, K. M., Park, Y., Kim, S.-R., & Son, K.-H. (2026). Modified white LEDs spectra alter tomato seedling quality and post-transplant responses. Discover Plants, 3, 530. https://doi.org/10.1007/s44372-026-01007-y